Re: [Bug-tar] tar 1.23: Problem under Solaris 10 - incorrect GNU header contents

[Joerg Schilling]

Tim Kientzle <address@hidden> wrote:

> If you're looking for details about tar formats,
> I wrote up a lengthy man page with a lot of
> details about tar format variants.
>
> There are online versions at the libarchive Wiki:
>
> http://code.google.com/p/libarchive/wiki/ManPageTar5
>
> and at the FreeBSD project man page reference:
>
> http://www.freebsd.org/cgi/man.cgi?query=tar&sektion=5&manpath=FreeBSD+8.0-RELEASE&format=html
>
> The mdoc-to-HTML translations seem to have some minor problems, though.
> If you don't have access to a FreeBSD system, you might find the
> mdoc source to be helpful:
>
> http://code.google.com/p/libarchive/source/browse/trunk/libarchive/tar.5
>
> In answer to your original question, the old "GNU tar" format
> violates the POSIX ustar specification in several respects.
> (GNU tar came out around the same time as the first POSIX
> specification.)  Most obviously, it sets the 8 bytes
> starting at offset 257 to:
>    'u' 's' 't' 'a' 'r' space space null
> where POSIX ustar archives set those same 8 bytes to:
>    'u' 's' 't' 'a' 'r' null '0' '0'
>
> The GNU tar format also does not use the ustar
> 'prefix' field as specified in POSIX and has non-POSIX
> extensions for handling long filenames, long linknames,
> and sparse files.  The mechanism used for sparse
> files, in particular, can cause tar implementations
> that don't understand this extension to lose header
> synchronization.

This is also explained in the star archive format man page

http://cdrecord.berlios.de/private/man/star/
http://cdrecord.berlios.de/private/man/star/star.4.html

BTW: star was the first tar archiver that implemented the 
POSIX.1-2001 archive format.

Jörg

-- 
 EMail:address@hidden (home) Jörg Schilling D-13353 Berlin
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